This invention relates in general to defect detection, and, in particular, to an improved system for detecting anomalies on surfaces, such as particles and surface-originated defects such as crystal-originated particles (“COPs”), surface roughness and micro-scratches.
The SP1TBI™ detection system available from KLA-Tencor Corporation of San Jose, Calif., the Assignee of the present application, is particularly useful for detecting defects on unpatterned semiconductor wafers. While the SP1TBI system provides unsurpassed defect sensitivity on bare wafers or unpatterned wafers, this is not the case when it is used for inspecting wafers with patterns thereon such as wafers with memory arrays. In this system, all of the radiation collected by a lens or ellipsoidal mirror is directed to a detector to provide a single output. Thus, since pattern on the wafer will generate Fourier and/or other strong scattering signals, when these signals are collected and sent to the detector, the single detector output becomes saturated and unable to provide information useful for detecting defects on the wafer.
Conventional techniques for detecting defects on wafers are either tailored for the inspection of patterned wafers, or for inspecting unpatterned or bare wafers, but not both. While inspection systems for detecting patterned wafers may be also used for inspecting unpatterned wafers, such systems are typically not optimized for such purposes. Systems designed for the inspection of unpatterned or bare wafers, on the other hand, may have difficulties handling the diffraction or other scattering caused by the patterned structures on patterned wafers, for reasons such as those explained above.
For the inspection of patterned wafers, entirely different inspection systems have been employed. One commercial system, known as AIT™ inspection system, is available from the Assignee of the present application, KLA-Tencor Corporation of San Jose, Calif.; such system is also described in a number of patents, including U.S. Pat. No. 5,864,394. In the AIT system, spatial filters are employed to shield the detectors from the diffraction or scattering from the patterned structures on the wafer. The design of such spatial filters can be based on prior knowledge of the patterned structures and can be quite complex. Furthermore, this system utilized a die to die comparison process in order better to identify the presence of a defect.
None of the above-described instruments is entirely satisfactory for the inspection of patterned wafers. It is therefore desirable to provide an improved defect detection system for patterned wafers in which the above difficulties are alleviated. To further economize on the space required for inline inspection, it is desirable to provide an instrument that can be optimized for both unpatterned and patterned wafer inspection.
Chemical mechanical planarization (CMP) has gained wide acceptance in the semiconductor industry. The CMP process, however, also creates many types of defects that can significantly impact the yield of an integrated circuit (IC) device if the defects are not properly controlled. Among the CMP defects, the micro-scratch has a strong impact on IC yield. Therefore, it is desirable to be able to detect and differentiate micro-scratches and other CMP defects from particles.
One important parameter for monitoring the quality of unpatterned or bare films on silicon wafers is the surface roughness. Surface roughness is typically measured by an instrument such as the HRP® instruments from KLA-Tencor Corporation, the Assignee of the present application, or by means of other instruments such as atomic force microscopes or other types of scanning probe microscopes such as scanning tunneling microscopes. One disadvantage of such instruments is the slow speed of their operation. It is therefore desirable to provide an alternative system which may be used for giving a measure of surface roughness at a speed much faster than the above-described instruments.